1. Field of the Invention
The present invention relates to an X-ray imaging technique.
2. Description of the Related Art
Conventionally, an X-ray imaging apparatus used in a hospital or the like uses a cassette. After an exposed cassette is developed, the developed film is interpreted by using an observation device called a film viewer. With the recent advances in digitization, image data are directly displayed as images on a monitor and observed without development of a film. These operations are performed to make examination and to observe the inner state of the body, for example, whether there is a tumor or the state of bone fracture.
In addition, recent X-ray imaging apparatuses have begun to be used as surgical auxiliary apparatuses instead of apparatuses for examination. For example, in executing cardiac catheterization, an operator generally performs treatment by tracking a catheter inserted into the body while observing radioscopic pictures. In this case, it is thought that puncturing operation can be effectively performed by capturing images by an X-ray imaging apparatus and superimposing/displaying visible images and radiographs as guide information for puncturing on a TV monitor so as to allow the operator to grasp a specific portion at which puncturing should be started. For example, Japanese Patent Laid-Open No. 54-158984 discloses an arrangement configured to superimpose and display radioscopic pictures and visible images on a monitor.
The technique disclosed in Japanese Patent Laid-Open No. 54-158984, however, is aimed at the examination of semiconductor wafers, and hence gives no consideration to changes in the relative positional relationship between an X-ray tube and an X-ray detection unit. Consider, for example, a nursing apparatus using an X-ray sensor (X-ray detection unit) called a cassette which can be arbitrarily placed. In this case, when the relative positions of the X-ray tube and X-ray sensor are changed, it is impossible to detect a positional shift. For this reason, the X-ray imaging apparatus cannot inform the user of the occurrence of the positional shift. As a consequence, the user must recognize the occurrence of the positional shift upon occurrence of an error in a capturing result, and position the X-ray sensor and the X-ray tube again.